Method of manufacture for projection television system

ABSTRACT

An article of manufacture is disclosed for use in a projection televison system. A cathode ray picture tube has a face panel with a rearwardly extending skirt and a window for receiving a cathodoluminescent imaging screen. The tube has a seal land which defines a plane whose normal makes a non-zero acute angle with respect to the axis of said window. The article is for use in a system having a cathode ray picture tube whose projection optical axis is on the axis of a remotely located viewing screen, and at least one displaced axis cathode ray picture tube; that is, a tube whose projection optical axis is displaced from the axis of the viewing screen by a non-zero acute angle. The method according to the invention provides for compensating for the non-linear magnification distortion of the projected image caused by the displacement of the tube off the viewing screen axis.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a division of application Ser. No. 154,197 filed May29, 1980, now U.S. Pat. No. 4,393,329, which in turn is acontinuation-in-part of application Ser. No. 110,413, filed Jan. 8,1980, now U.S. Pat. No. 4,274,110. This application is related to but inno way dependent upon copending application Ser. No. 127,603, filed Mar.3, 1980, now abandoned, all of common ownership herewith.

BACKGROUND OF THE INVENTION AND PRIOR ART DISCLOSURES

This invention is concerned with television systems, and is particularlydirected to projection television systems in which discrete images areprojected on a projection screen to provide a composite color picture.

FIG. 1 is a schematic plan view of the essentials of a representativeprior art projection television system 6 in which a bank 8 of lightprojection devices 10, 12 and 14 project through the indicatedassociated lens means blue, green and red images, respectively, on aremotely located projection screen 16. The projected images are intendedto form a composite color image. Projection screen 16, which may beeither of the front-projection or rear-projection type, typically has anaspect ratio of 3:4 in consonance with the aspect ratio of the standardtelevision picture.

The centrally located device 12 typically has its projection opticalaxis 18 in congruence with screen axis 20, and as a result projects anundistorted light image on projection screen 16. The light imagesprojected by devices 10 and 14, however, whose projection optical axis22 and 24 respectively are located "off-axis" with respect to projectionscreen axis 20, inherently project light images which are distortedbecause of their off-axis location.

Two types of optical distortion are inherent in the system which candegrade through misconvergence the composite projected image to thepoint of unacceptability. The types are trapezoidal distortion andhorizontal non-linearity, and they can best be described by the singleterm "non-linear magnification distortion." As noted, the light imageprojected by the centrally located device 12 is not subject tonon-linear magnification distortion because its projection optical axis18 is congruent with the projection screen axis 20. As a result, thelight image projected on projection screen 16 will by symmetrical andundistorted. The light image projected by device 12 is typically thatshown in FIG. 2 by light image 26, indicated as being rectilinear.

This is not so with the light images as projected by devices 10 and 14.The inherent distortion of the light images due to the off-axis locationis depicted by FIG. 2, wherein the light image projectedby device 10 isindicated by configuration 28 as being trapezoidal. Similarly, the imageprojected by device 14 is indicated by configuration 30 as beingtrapezoidal. In a typical prior art projection television system, thenon-linear magnification distortion may be of the order of five percent,an amount sufficient to so misregister the images as to render thecomposite picture unacceptable to the viewer.

It is to be noted that if the projection devices 10, 12 and 14 arevertically stacked, a similar distortion will be realized in the case ofdevices 10 and 14. The non-linear magnification distortion realized isdescribed in the context of this disclosure, as "keystoning" distortion,rather than "trapezoidal" distortion.

The second form of distortion--horizontal non-linearity--is also inconsequence of the location of devices 10 and 14 off the projectionscreen axis 20. The effect of this type of distortion is depicted inFIG. 3, using as an exaple the light image 28 projected by lightprojection device 10, indicated as being trapezoidal due to theaforedescribed non-linear magnification distortion (the trapezoidalshape is exaggerated for the purpose of illustration). The lines 32A-Grepresent the vertical lines of a television screen cross-hatchgenerator, as projected. The effect of horizontal non-linearitydistortion is apparent in the progressive increase from left to right inthe distance between lines 32A-G. The vertical lines of the light image30 projected by device 14 would be similarly distorted, but in theopposite direction.

One approach to the correction of trapezoidal distortion is byelectronic means. For example, the image projected by the off-axiscathode ray tubes of projection means 10 and 14 can be madecompensatorily trapezoidal. This can be done by synthesizing acorrection wave form for application to a high-speed writing-type yokewhich is placed in tandem with the main deflection yoke. The end resultis a trapezoidally shaped raster inverse in orientation to the normaldistortion of the image projected by the off-axis cathode ray tubes ofprojection means 10 and 14. Correction by such electronic means isplagued by the complications introduced in the television circuit, witha consequent increase in cost. The complexity and added cost is evengreater in consequence of the fact that the correction circuitry for thetwo off-axis CRT's must be dsigned to exert an opposite effect on theirprojected images. The economic burden imposed by the electronic approachis further underscored in view of the fact that while it may beeffective against trapezoidal distortion, it is largely ineffective interms of correction for horizontal non-linearity distortion, whereinadditional and very complex electronic correction circuitry must beemployed.

Optical systems for reducing or otherwise ameliorating distortioninclude Oland--U.S. Pat. No. 4,004,093, which discloses a truncatedSchmidt optical system wherein a plurality of Schmidt systems areclustered closely together by truncating the mutually adjacent edges ofmirors and correcting lenses which comprise individual Schmidth systems.Such clustering is said to provide a reduction in trapezoidal distortionby virtue of the fact that the cathode ray tubes for each primary colorproject images which arrive almost orthogonally at the screen.

Hergenrother et al.--U.S. Pat. No. 4,024,579--discloses a projectiontelevision system in which the composite image is projected onto acurved screen by three discrete cathode ray tubes arranged as a triad,with each projecting a different primary color. The tube optics arefolded into a catadioptric configuration and the three images are causedto converge into a composite image by an elaborate optical system thatincludes a Schmidt correction lens mounted externally to the envelope ofeach tube. Although the system has achieved a measure of consumeracceptance, the need for an extensive alignment procedure to achieve asatisfactory composite image, and the general lack of brilliance of theprojected image, has limited its acceptance.

It is known in the art that if the axis of an electron gun is at anangle with respect to the axis of a cathode ray tube, the visible imageon the face panel will exhibit non-linear magnification distortion. Thistype of distortion was common to certain early image iconoscope tubes ofVladimir Zworykin and was considered a performance liability. An exampleof a cathode ray tube configuration having an electron gun at an anglewith respect to the tube axis is shown in U.S. Pat. No. 2,777,084 toLafferty.

Pat. No. 28 37 249 (German) discloses a system for optically correctingtrapezoidal distortion of the image projected by cathode ray tubeslocated off a central axis. The projection system includes cathode raytube color picture sources, ech of which projects its image through aprojection lens. Trapezoidal distortion is stated as being corrected bytilting the picture sources away from the central axis relative to thelight axis of the associated projection lens. As a result, the image onthe faceplate of the cathode ray tube is no longer parallel with thescreen. When the image on the cathode ray tube faceplate is projected,the image on the screen is reputed to be parallel.

Ohmori, in U.S. Pat. No. 4,194,216, discloses a video projectionapparatus having a plurality of cathode ray tubes and associatedprojection lenses. The apparatus includes a projection lens and a halfmirror common to a red and blue cathode ray tube. The projection lensesare arranged so that their optical axes are parallel with each other andperpendicular to the viewing screen. As a result, the projected imagesare displaced to the right and left of the center of the screen. Thisdisplacement is said to be correctable by outwardly and epaxiallydisplacing the cathode ray tubes with respect to the optical axes.However, trapezoidal distortion of the hitherto misaligned, now aligned,images results. This distortion is stated to be corrected by incliningthe displaced axis tubes outwardly. This inclination, in conjunctionwith the refractive index of the glass face plates of the cathode raytubes, is said to correct the trapezoidal distortion.

Examples of circuit means intended to provide convergence of multiplecolor image projectors are to be found in the following U.S. Pat. nos.

Seright--2,654,854

Mengle--2,989,584

Austefjord--3,943,279

OBJECTS OF THE INVENTION

It is a general object of the invention to provide for improvedperformance in certain projection television systems.

It is another object of the invention to provide for improvedperformance in projection television systems having off-the-axis imageprojection devices.

It is yet another object of the invention to provide for a reduction inthe cost of projection television systems in terms of enhancedsimplicity in design, easier set-up, and minimized need for electronicdistortion-correction circuitry.

It is a more specific object of the invention to provide for theelimination of trapezoidal distortion in off-optical axis imageprojectors in projection television systems.

It is a specific object of the invention to provide for the simultaneouscorrection of trapezoidal distortion and horizontal non-linearitydistortion in projection television systems by purely mechanical means.

It is another specific object of the invention to provide an improvedmethod for manufacturing components providing for self-convergence incertain projection television systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings, in the several figures ofwhich like reference numerals identify like elements, and in which:

FIGS. 1-3 show diagramatically the cause and effects of the two types ofnon-linear magnification distortion experienced in certain prior artprojection television systems;

(The following FIGS. 4-12 are shown in referent U.S. Pat. No. 4,274,110.These drawings and associated descriptions are considered necessary forthe understanding of the present invention.)

FIG. 4 is a highly simplified schematic view of a projection televisionsystem having off-axis light projection means;

FIG. 5 shos diagrammatically and in greater detail one such off-axisprjection means;

FIG. 6 is a schematic view in perspective showing the beneficial effectof the FIG. 5 embodiment;

FIG. 7 is a simplified view in perspective of a projection televisionsystem having three light projection means;

FIG. 8 is a view in elevation of an array of nine image-projectiondevices;

FIGS. 9 and 10 are schematic views of further embodiments of cathode raytube components;

FIGS. 11 and 12 indicate diagrammatically the relative positions andorientations of an array of light-projection components;

FIGS. 13A-C are schematic views illustrating the method of formingcathode ray tube components according to the present invention; FIG. 13Ddepicts schematically a standard cathode ray tube for comparisonpurposes;

FIGS. 14A-14B are diagrams in section of cathode ray tube componentsmanufactured according to the invention; FIGS. 14C-14D indicateschematically the effect of the respective components on theelectron-formed visible image;

FIGS. 15A-15B are schematic view of a cathode ray tube componentmanufactured according to the invention having a rectangular face panel;and,

FIG. 16 shows schematically a cathode ray tube component according tothe invention having a square (equilateral rectangular) face panel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 4 there is depicted schematically a projection television system70. The system 70 has a viewing screen 72 for displaying a light imagecast thereon. Screen 72 is remotely located from a plurality of lightprojection means 74. At least one light projection means, designated asbeing projection means 76, has a projection optical axis 78 at anon-zero, acute-angle A with respect to the viewing screen axis 80.

With reference also to FIG. 5 wherein projection means 76 is depicted ingreater detail, projection means 76 is indicated as including a cathoderay tube means 82 having a cathodoluminescent screen 84 on the insidesurface of the face panel 86 whose axis is substantially parallel to theprojection optical axis 78. The seal land 85 indicates the junction ofthe face panel 86 and the funnel 87 of cathode ray tube 82; thesignificance of the seal and its orientation will be described infra.The screen is made cathodoluminescent by a deposite of a monochromephosphor which may comprise, for example, one of a number of phosphorsemitting red, green or blue light upon excitation by an electron beam.The electron beam generating means 88, which is typically an electrongun, is disposed on the electron-optical axis 90 of cathode ray tube 82.Electron beam generating means 88 is indicated as emitting a scanningelectron beam 92 which forms an electron image on the cathodoluminescentscreen 84 in response to television signal information. The electronimage is converted to a visible image by cathodoluminescent screen 84 asscreen 84 is excited by beam 92.

Lens means 94 on projection optical axis 78 provides for projecting onviewing screen 72 the light image of the electron-formed visible imageon cathodoluminescent screen 84. The light image inherently has anon-linear magnification distortion attributable to the location ofprojection means 76 off the viewing screen axis 80.

The non-linear magnification distortion of the light image as projectedon viewing screen 72 is shown in FIG. 4 as being trapezoidal, asindicated by the dash-line image 98. Horizontal non-linearity distortionis also present as described heretofore.

The projection television system according to the invention describedand fully claimed in the referent '110 patent is characterized by theelectron-optical axis 90 of cathode ray tube means 82 defining anon-zero, acute-angle B with respect to the axis of cathodoluminescentscreen 84. The value of angle B and the orientation of theelectron-optical axis is selected to cause the electron-formed visibleimage to have an orientation and non-linear magnification distortioneffective to substantially compensate for the off-axis-inducednon-linear distortion of the projected light image.

The remedial effect is depicted in FIG. 6, which is view looking overthe screen 72 and toward the face panel 86 of light projection means 76.An electron-formed visible image 104A, depcited as being trapezoidal hasan orientation and non-linear magnification distortion effective tosubstantially compensate for the off-axis-induced non-linearmagnification distortion of the projected light image. Image 104A isshown as being reversed in orientation by transmission through lensmeans 94; the shape of the image in space as projected on viewing screen72 is indicated by light image 104B. It will be seen that image 104Asubstantially compensates for the off-axis-induced non-linearmagnification distortion, as indicated by image 104C cast on viewingscreen 72, depicted as being substantially free of non-linearmagnification distortion.

A bank of three light projection means for use in a projectiontelevision system is shown by FIG. 7 (and by FIG. 8, as will be noted).Bank 106 comprises light projection means 108, 110 and 112 forprojecting, by way of example, red, green and blue images, respectively,to form a composite color image in space. A viewing screen 114 providesfor receiving the composite color image 116, the perimeter of which isindicated by the dash lines.

Light projection means 108, 110 and 112 comprise, respectively, cathoderay tube means 126, 128 and 130, and associated lens means 126A, 128Aand 130A. Each tube has a cathodoluminescent screen indicated, againrespectively, by 126B, 128B and 130B disposed on the inside surface ofthe face panel thereof. Each light projection means has electron-beamgenerating means disposed on an associated electron-optical axis 126C,128C and 130C for forming an electron image on the associatedcathodoluminescent screen; the electron images are converted to visibleimages by the respective cathodoluminescent screens. Lens means 126A,128A and 130A provide for projecting on viewing screen 114 the lightimages of respective electron-formed visible images to form compositecolor image 116.

Light projection means 110 is shown as being "on-axis;" that is, itselectron optical axis 128C is congruent with its projection optical axis120. As a result, the electron-formed visible image 128D formed on itsscreen 128B is rectilinear. Also as a result, the light image 128E thatit projects is rectilinear and the light image cast on the screen isrectilinear and in coincidence with the composite color image 116, ofwhich it forms a part.

Light-projection means 108 and 112, however, project a light imageinherently having non-linear magnification distortion attributable totheir location off the projection screen axis 120. These may be termed"displaced-axis" tubes. This inherent distortion is compensated for bythe electron-optical axes 126C and 130C of the respective cathode raytube means 126 and 130 each defining a non-zero, acute-angle B withrespect to the axes of the associated cathodoluminescent screens 126 Band 130B. The value of angles B and the orientation of theelectron-optical axes is selected to cause the electron-formed visibleimages 126D and 130D to have an orientation and non-linear magnificationdistortion effective to substantially compensate for theoff-axis-induced non-linear magnification distortion of the projectedlight images. The projected light images are indicated as beingtrapezoidal images 126E and 130E, respctively, as projected bylight-projection means 108 and 112. The projected light images 126E and130E, when cast on viewing screen 114 are substantially free ofnon-linear magnification distortion, and are indicated as being mutuallycoincident with the rectilinear composite color image 116.

The projection system described can comprise a bank of threelight-projection means oriented side-by-side in a horizontal plane. Thisembodiment is indicated by the three light-projection means comprisingbank 144 of FIG. 8. Alternately, the light projection means could aswell comprise a vertical stack, as indicated by the light-projectionmeans of column 150.

FIG. 8 shows an array 140 of three banks 142, 144 and 146 of lightprojection means for projecting a very bright composite image.(Associated lens means are not shown.) Each bank consists of three lightprojection means for projecting into coincidence with adjacent lightprojection means red, green and blue images, respectively. The order ofthe color images is exemplary only, and not limiting. The column 148 oflight projection means may, for example, project red images; centercolumn 150 may project green images, and column 152, blue images, toform the composite color image in space. A remotely located viewingscreen (not shown) receives and displays the composite color image.

Each light projection means in array 140 comprises a cathode ray tubemeans having a cathodoluminescent screen on the inside surface of theface panel thereof whose axis is substantially parallel withitprojection optical axis. Electron-beam generating means are disposedon the cathode ray tube electron-optical axis for forming an electronimage on the cathodoluminescent screen which is thereby converted to avisible image. The lens means (not shown) provide for projecting on theviewing screen a light image of the electron-formed visible image thatis on the cathodoluminescent screen. As described heretofore with regardto other configurations of projection television system, the lightimages of off-axis-located cathode ray tubes inherently have non-linearmagnification distortion attributable to the location of the projectionmeans off the projection screen axis. The array projection system ischaracterized by the cathode ray tube electron optical axis of each ofthe off-axis projection means defining a non-zero, acute angle withrespect to the axis of the cathodoluminescent screen. The value of theangle and the orientation of the electron-optical axis is selected tocause the electron-formed visible image to have an orientation andnon-linear magnification distortion effective to compensate for theoff-axis-induced non-linear magnification distortion of the projectedlight image.

The electron-formed visible images of the off-axis cathode ray tubes ofthe nine-tube array shown by FIG. 8 are effective to substantallycompensate for the off-axis location of the respective cathode raytubes. Image A, projected by a center tube, whose projection opticalaxis is congruent with the screen axis, is shown as being non-distorted,and when projected, will form a rectilinear image on the projectionscreen. The images B and C of the adjacent off-axis cathode ray tubesare shown as being trapezoidal and keystone-shaped, respectively, butwhen projected will substantially compensate for the off-axis-inducednon-linear magnification distortion of the projected images. Images D ofthe corner cathode ray tubes, which may be termed "scalenequadrilaterals," similarly compensate for the off-axis location of theassociated cathode ray tubes. The result is that the red, green and blueimages when projected form a composite color image in space wherein anynon-linear magnification distortion due to off-axis location issubstantially compensated for. (It must be remembered that theassociated lens means reverse the images.)

An array of light-projection means, shown as numbering nine in FIG. 8,may comrpise a lesser number. For example, the array may comprise twobanks, such as banks 142 and 144, or, banks 144 and 146.

FIG. 9 depicts another embodiment wherein a cathode ray tube 154comprising a component of a light-projection means for a projectiontelevision system has a face panel 156 and associated cathodoluminescentscreen disposed on the projection optical axis 160. The projectionsystem is characterized by the electron-beam axis 162 defining anon-zero, acute-angle B with respect to the projection optical axis 160.The value of angle B and the orientation of the electron-beam axis 162is selected to cause the electron-formed visible image oncathodoluminescent screen 158 to have an orientation and a non-linearmagnification distortion effective to substantially compensate for theoff-axis-induced non-linear magnification distortion of the projectedlight image.

Another configuration of a projection system cathode ray tube is shownby FIG. 10, wherein the axis 157 of the electron-beam generating means159 defines a non-zero, acute-angle B with respect to the projectionoptical axis 161. The neck 163, which encloses electron-beam generatingmeans 159, is shown as extending at a non-zero, acute-angle B from ahemispherical funnel section 165. It should be noted that the angle Bdepicted is exaggerated for illustrative purposes; the non-zero,acute-angle B in this and all figures is, as a general rule in the rangeof a nominal 3 to 9 degrees. This range is provided for example only,and is not a limitation.

A method for compensating for the non-linear magnification distortion ofthe image projected by a light projection means whose projection opticalaxis is oriented off the projection screen axis comprises the following.A cathode ray tube is provided which includes associated projection lensmeans; these components comprise the light projection means. The cathoderay tube has a cathodoluminescent screen on the inside surface of theface panel thereof whose axis is substantially parallel to theprojection optical axis. An electron-beam generating means is disposedon an electron-optical axis of the cathode ray tube for forming anelectron image on the cathodoluminescent screen which is converted to avisible image by the cathodoluminescent screen. The cathode ray tubeelectron-optical axis is positioned so as to define a non-zero, acuteangle with respect to the axis of the cathodoluminescent screen. A valueof the angle and an orientation of the electron-optical axis is selectedto cause the electron-formed visible image to have an orientation andnon-linear magnification distortion effective to substantiallycompensate for the off-axis-induced non-linear magnification distortionof the projected light image. Alternately, the method may comprise thepositioning of the cathode ray tube electron-optical axis so as todefine a non-zero, acute angle with respect to the projection opticalaxis.

Here follows a description for utilizing the means in a projectiontelevision system. It is to be recognized that the means described areby way of example only, and that other arrangements and configurationswill readily occur to those skilled in the art.

The cathode ray tube means preferably comprise round face panel tubeshaving a face panel diameter of about 5 inches. The face panels of oneor more of the tubes used in a multiple-tube system could as well berectangular or square, if desired. The monochrome phosphor, whether red,green or blue, deposited on the cathodoluminescent screen that convertsthe electron image to a visible image, is preferably a high-emissiontype for optimum image brightness; such phosphors are well known in thepresent art. The cathode ray tube deflection angle is preferably about70 degrees, an angle which provides a short-necked tube which permitsdisplay cabinet depth reduction in tight packaging concepts.

The electron gun is preferably of the high-performance type, one thatwill produce a small beam spot with minimum spot blooming at high beamcurrents to provide good resolution. For maximum brightness, the ultoranode voltage is preferably in the range of 28-30 kilovolts. Thestandard CRT electron gun configurations--the bipotential, theunipotential, or the extended field lens--all lend themselves readily toapplication in projection television systems.

A salient benefit of the system is that a relatively simple,uniform-field deflection yoke can be used; the yokes can be identicalfor all cathode ray tubes in the projection system. Because there is noneed for elaborate electronic circuits to correct for trapezoidaldistortion, the secondary high-speed writing yoke normally mountedbehind the deflection yoke in certain prior art projection systems isnot required.

The lens means, one of which is associated with each cathode ray tube,may comprise for example, an aspheric, three-element lens having coatedsurfaces, and preferably a five-inch focal length. For maximumbrightness of the projected image, the lens should be of the high-speedtype of F1.0 or less. The lens is preferably permanently mounted inconjunction with its associated cathode ray tube, so no adjustments willbe necessary either in factory or field.

A bank of light-projection systems arranged for side-by-side mounting ina horizontal plane, as depicted by FIG. 7, can be mounted permanentlyand without the need for adjustment on a rigid metal bed. Once mounted,no mechanical adjustments in azimuth or elevation will be necessary.

It has been observed in connection with FIG. 7 that the electron-opticalaxis 128C of light projection means 110 is congruent with its projectionoptical axis 120. The light projection means 108 and 112 adjacent tolight projection means 110, however, lie off-axis; that is, theirprojection optical axes 122 and 124 lie at non-zero acute-angles A withrespect to the projection screen axis 120, as indicated. The electron-optical axes of each off-axes projection means 108 and 112 define anon-zero, acute-angle B with respect to the screen axes 120. Thenon-zero, acute-angle A may be, for example, about seven degrees. Thenon-zero, acute angle B may also be about seven degrees, and as ageneral rule, angle A and B may be considered to be equal. The value ofangle B and the orientation of the electron-optical axes is selected andis effective to provide an electron-formed visible image configured andoriented to substantially compensate for the aforedescribed off-axisinduced trapezoidal distortion. The angle values cited are in no waylimiting. Angles in the range of three to nine degrees, or greater orlesser, could as well be utilized, with the selection of the particularangle made on the basis of the requirements of a particular projectionsystem. (Other angle values will be cited infra). Factors in thedetermination of the proper angles include the location of the off-axistube, focal length of the lens, the magnification of the lens, the sizeof the projection screen, and the distance between the light projectionmeans and the projection screen, and the distance the off-axis tubes arefrom the screen axis.

The viewing screen of the preferred embodiment is 50 inches in diagonalmeasure, and the aspect ratio is 3:4, in consonance with the standardtelevision picture format. The distance from the electron image on thecathodoluminescent screen of the cathode ray tube is typically 58.3inches. The screen may be either a rear projection type or a frontprojection type. Gain is normally built into the screen to provide addedbrightness; the gain factor may be as great as 10.

The optical path of the projection system may be "folded;" that is,mirrors may be used between the light projection means and theprojection screen so that the projection system can be embodied in arelatively small cabinet. Adjustments in the location of the image onthe projection screen can be accomplished by tilting of one or more ofthe mirrors by simple mechanical means known in the art.

Adjustments for static convergence of the discrete monochrome imagesthat make up a composite color image, as well as other adjustments suchas horizontal sweep, can be accomplished with standard televisionreceiver circuits in present use.

The high-brightness projection television system described isessentially a self-converged system and therefore requires only staticconvergence; that is, horizontal and vertical centering. There is norequirement for purity set-up since the shadow mask is not used in theprojection tubes. Horizontal and vertical centering is required toobtain coincidence of the three image centers. The position on theviewing screen and the size of the green picture image is firstestablished. Then the height and width of scan of the red and blue imageprojection devices is established to provide registration of the threeimages.

As indicated by FIG. 11, the face panels of all cathode ray tubes of anarray (whatever the number in the array, whether three, four, six ornine, e.g.) are positioned with respect to the screen on a sphericalsurface with a radius R; that is, the center of each face panel isperpendicular to a sphere radius R extended from the center of theprojection screen. The spatial relationship of the face panels of anarray of nine cathode ray tubes is shown by FIG. 12. If a sphere radiusR is drawn through the centers of the face panels 170A, 170B, 170C and170D on a radius x from the center point of the array, a right circularcone is generated whose base is indicated by 172, and whose apex is thecenter of the projection screen. Face panels 170A-D are off theprojection optical axis by the same angular magnitude. This is theaforedescribed non-zero, acute-angle A. The face panels 174A, 174B, 174Cand 174D, however, are on a radius (R=x√2) with respect to the center ofthe array, and the non-zero, acute-angle formed with respect to thesenear or on-diagonal tubes is a complex angle having both horizontal andvertical components relative to the axis of the cathodoluminescentscreen. The base of the right circular cone on which face panels 174A-Ddepend is indicated by reference number 176.

It may be assumed that a plurality of different face panel-funnelconfigurations may be required, especially in multiple-cathode ray tubearrays such as depicted in FIG. 8. While each configuration could becast in its own separate, distinct glass mold, the cost would beprohibitive. It is more practical and far less costly to use the methoddescribed herein.

A cathode ray picture tube 180 for use in a projection television systemis depicted schematically in FIGS. 13A-C. The projection optical axis190 of tube 180 is displaced from the axis of a remotely located viewingscreen (not shown) by a non-zero acute angle A. 1 (Please refer to FIG.4 for an example of a cathode ray tube 76 whose projection optical axis78 is displaced from the viewing screen axis 80 by said angle A.)Picture tube 180 is shown as having a conjoinable face panel 182 with arearwardly extending skirt 184 and a funnel 185. The skirt 184 of panel182 mates along interfacing funnel seal edge 186 and face panel sealedge 188.

Tube 180 has a cathodoluminescence imaging screen 183 deposited on theinner surface or "window" of face panel 182; the axis of the window (andcathodoluminescent screen) is substantially coincident with theelectron-optical axis 187, and normally coincident with projectionoptical axis 190. Imaging screen 183 provides an electron-formed visibleimage for projection on the viewing screen.

Funnel seal edge 186 is formed as depicted to define a plane whosenormal makes an angle (designated at being angle C) with respect to thefunnel axis 189 substantially equal to one-half of the aforedescribedangle A. Seal edge 188 of face panel 182 is formed to define a planewhose normal makes an angle (also indicated as being an angle C) withrespect to the axis of the imaging screen 183, or window, substantiallyequal to one-half said angle A.

Funnel 185 is aligned according to the invention with respect to facepanel 182 to tilt the electron-optical axis 187 with respect to theprojection optical axis 190 by an angle B substantially equal to saidangle A; this configuration is shown by FIG. 13B. When seal edges 186and 188 are conjoined, forming seal land 192, the value of angle B andthe orientation of the electron-optical axis 187 causes theelectron-formed visible image on cathodoluminescent screen 183 to havean orientation and non-linear magnification distortion effective tosubstantially compensate for the off-axis-induced, non-linearmagnification distortion of the light image projected thereby on theviewing screen.

An article of manufacture for use in a projection television systemcomprises a cathode ray picture tube 180 having a face panel 182 with arearwardly extending skirt 184 and a window for receiving acathodoluminescence imaging screen 183. The panel skirt 184 isconjoinable with funnel 185 by mating along interfacing edges. The edgeof the skirt 184 defines a plane whose normal makes a non-zero acutecant angle with respect to the axis of the window. The funnel edgedefines a plane whose normal makes a non-zero acute cant angle withrespect to the funnel axis 189. Thus the funnel can be aligned andconjoined with the face panel to define a selected tilt angle withrespect to the axis of the window. When the interfacing edges areconjoined as by frit sealing, the tube has a seal land which defines aplane whose normal makes a non-zero acute angle with respect to the axisof the window. As depicted by FIG. 13B, funnel 182 is, in effect,aligned by its "rotation" with respect to face panel 184 a distanceeffective to provide the non-zero acute angle B having a desired value.The non-zero, acute angle B is that angle which is substantially equalto the aforedescribed angle A. The "rotation" of funnel 182 with respectto face panel 184 is typically about 180 degrees.

FIG. 13D depicts for comparison purposes a standard cathode ray tubewherein the interfacing edges (the conjoining of which is indicated byseal land 194) define a plane whose normal is coincident with theprojection optical axis 196.

With reference again to FIG. 8, a cathode ray tube having theaforedescribed characteristics; that is, wherein the value of angle B is4.74 degrees, by way of example, could be used in the off-axis imagedisplay means locations of both bank 144 and row 150 which projectelectron-formed visible images B and C, respectively. However, thecathode ray tubes used in the off-axis image display means which projectelectron-formed visible images D, would necessarily have a differentvalue of angle B. As described in connection with FIG. 12, the facepanels 174A-D are on a different radius (R=x√2) than the face panels170A-D (radius x). For example, if angle B is 4.74 degrees for imagedisplay means having face panels located on a radius x (face panels170A-D), the value of the angle B of the display means whose face panelsare located on a radius R=x√2 (face panels 174A-D) would be 6.67degrees.

One pair of glass molds can be utilized for the manufacture of both anon-axis tube and a displaced-axis tube, while providing for thecompensating for the non-linear magnification distortion of theprojected image of the displaced-axis tube. A projection televisionsystem of this type is depicted in FIG. 7, wherein an on-axis tube 110is shown in conjunction with two such displaced-axis tubes 108 and 112.The method comprises the following, with reference again to FIGS. 13A-C.(Both of the displaced axis tubes 108 and 112 are considered as being oflike construction.)

The funnel seal edges 186 of both the on-axis tube (of which there canbe only one) and a displaced-axis tube are formed by a funnel mold todefine planes whose normal makes an angle substantially equal toone-half the angle A with respect to the funnel axis. Similarly, theface panel seal edges 188 of the on-axis tube and a displaced-axis tubeare formed by a face panel mold to define planes whose normal makes anangle substantially equal to one-half the angle A with respect to theface panel axis. The funnel of the displaced-axis tube is aligned withrespect to its face panel to tilt the electron-optical axis 187 withrespect to the projection optical axis 190 by an angle B substantiallyequal to angle A. This configuration is depicted by FIG. 13B. The funnelof the on-axis tube is aligned and conjoined with respect to its facepanel so that the electron-optical axis 194 is coincident to theprojection optical axis 190. This configuration is depicted by FIG. 13C.The seal edges 186 and 188 of the respective tubes are then conjoinedforming seal land 192. The face panels and funnels of both the on-axistube and the displaced axis tube can be formed by one pair of glassmolds. Thus one pair of the aforedescribed glass molds can be used toform the face panels and funnels of the cathode ray tubes in bank 144and row 150 depicted by FIG. 8.

It will be observed that the face panel itself of a displaced-axis tubeis not tilted per se, but that the remainder of the tube; that is, thefunnel and neck which are aligned on the electron-optical axis, are moreproperly termed as being tilted with respect to the face panel. Thischaracteristic will be noted with regard to FIG. 8 wherein therespective necks n of the cathode ray tubes other than the center,on-axis cathode ray tube 168; that is, those providing electron-formedvisible images B, C and D, will be observed to be directed at anglesoutwardly from the center, with the electron-optical axes of the cathoderay tubes providing images B lying in the horizontal plane and with theaxes of those providing images C lying in the vertical plane.

A second pair of molds is required for the cathode ray tubes shown inFIG. 8 which are on diagonals with respect to the center cathode raytube 168; these are the cathode ray tubes providing electron-formedvisible images D. The requirement for a second pair of molds is based onthe fact that the respective angles B are different as describedheretofore; i.e., angle B for the tubes in bank 144 and column 150(radius=x) is described as being 4.74 degrees, while the angle B for thetubes located on the diagonal (radius-√2) is described as being 6.67degrees.

The respective necks n of the CRT's providing images D lie at an angleof essentially two times angle B with respect to the horizontal axis.After providing the proper angle B, noted for example as being 6.67degrees for the diagonally located CRT's exhibiting images D, the CRT'sare rotated from the horizontal plane to provide an angle essentiallytwo times angle B to provide images D of the scalene quadrilateral shapeindicated which, when projected, compensate for the off-axis, diagonallocation of the cathode ray tubes providing images D.

The embodiments of the projection tube manufactured according to theinvention shown schematically by FIGS. 13A-C are depicted in morerealistic detail in FIGS. 14A-B. With specific reference to FIG. 14A, inwhich an on-axis tube is depicted, face panel 182 cathodoluminescentscreen 183, and funnel 185 of cathode ray tube 180 are shown. Spliceline 192 represents the conjoining of the interfacing edges of funnel185 and face panel 182. The funnel 185 is aligned with respect to itsface panel 182 such that the electron-optical axis is coincident withthe projection optical axis 190. There is indicated additionally a neck202, a flare 204 and an anode button 206. The yoke reference line 208,deflection center 210, and a neck splice line 212 are also indicated.The angle of deflection 214 of the electron beam (not indicated) fromdeflection center 210 is preferably 70 degrees. The electron-formedvisible image 216 is indicated in FIG. 14C as being rectilinear in shapeand essentially occupies an area on face panel 184 as depicted. Theminimum useful screen area for the visible image 216 comprises an areaof circular face panel 182 of three inches by four inches, with afive-inch diagonal.

Alignment ribs 218 and 220 are embossed 180 degrees apart on the flange222 of face panel 182. Alignment ribs 224 and 226 are located adjacentlyto ribs 218 and 220, respectively. The alignment ribs provide foraccuracy in the aforedescribed aligning of the funnel 185 according tothe invention with respect to its face panel 182.

The dimensions in inches of the cathode ray tube 180 depicted by way ofexample in FIG. 14A may be as follows. All dimensions and values citedin the following, as well as those in other parts of the specification,are provided by way of example only, and are intended to be in no waylimiting. Changes in dimensions and configurations will no doubt occurto those skilled in the art--changes which are yet within the scope andcompass of the invention.

    ______________________________________                                        diameter of face panel 182                                                                          6.25                                                    overall length of CRT 180                                                                           11.25                                                   O.D. of neck 202      1.125                                                   I.D. of neck 202      0.955                                                   distance between face panel and -                                                                   3.65                                                    yoke reference line 208                                                       deflection center 210 3.97                                                    thickness of face panel 182                                                                         0.400                                                   ______________________________________                                    

The value of the respective angles B and C in degrees may be, forexample (please refer to FIG. 13B):

Angle B: 4.74

Angle C: 2.37

FIG. 14B depicts a displaced-axis tube of like construction and havingthe same basic dimensions as the aforedescribed on-axis tube. The funnel185 is aligned with respect to its face panel such as to tilt theelectron-optical axis 187 with respect to the projection optical axis190 by an angle B. The electron-formed visible image 216A is displacedin a measure; however, it remains within the field of thecathodoluminescent screen 183. The beneficial non-linear magnificationdistortion of the image 216A resulting from application of the inventionis shown by FIG. 14D.

An example of a displaced-axis cathode ray tube 244 having a neck 246, afunnel 248 and a substantially rectangular face panel 250 in lieu of theround face panel hitherto depicted and described is shown schematicallyby FIGS. 15A-B. The electron-optical axis 252 of cathode ray tube 244 iscaused to define a non-zero, acute angle B (shown greatly exaggerated)with respect to the cathodoluminescent screen axis 254 by the methodaccording to the invention. The resulting electron-formed visible image256 (see FIG. 15B) has an orientation and a non-linear magnificationdistortion effective to substantially compensate for theoff-axis-induced non-linear magnification distortion of the projectedlight image. The configuration of cathode ray tube 244 could be used inthe location occupied by cathode ray tube 170, shown by FIG. 8; and ifcathode ray tube 244 is inverted, in place of cathode ray tube 166.

The face panel could as well be of "square" configuration (anequilateral rectangle), as shown by FIG. 16, in which face panel 260 isshown as displaying an electron-formed visible image 262 similar toimage 256 displayed by face panel 250 depicted by FIG. 15B. Alsosimilarly, a cathode ray tube having a square face panel 216 could beused when properly oriented as noted in the location occupied by eithercathode ray tube 166 or 177 shown by FIG. 8. Both the rectangular andthe square cathode ray tube panel configurations can, when properlyoriented, as well be used in place of the cathode ray tubes displayingimages B in bank 144 of FIG. 8.

While particular aspects of the inventive method have been shown anddescribed, it will be obvious to those skilled in the art that changesand modifications may be made without departing from the invention inits broader aspects, and therefore, the aim of the appended claim is tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:
 1. For use in the manufacture of a projection television systemhaving at least one cathode ray picture tube whose projection opticalaxis is displaced from the axis of a remotely located viewing screen byan angle A, and with a cathodoluminescent imaging screen whose axis issubstantially coincident with said projection optical axis and normallycoincident with the electron-optical axis of said tube, said imagingscreen providing an electron-formed visible image for projection on saidviewing screen, said cathode ray picture tube having a conjoinable facepanel and funnel which mate along interfacing edges, a method forcompensating for the non-linear magnification distortion of theprojected image caused by the location of said tube off the viewingscreen axis, comprising:forming the seal edge of said funnel to define aplane whose normal makes an angle with respect to the funnel axissubstantially equal to one-half said angle A; forming the seal edge ofsaid face panel to define a plane whose normal makes an angle withrespect to the imaging screen axis substantially equal to one-half saidangle A; aligning said funnel with respect to said face panel to tiltsaid electron-optical axis with respect to said projection optical axisby an angle B substantially equal to said angle A; and conjoining saidseal edges;such that the value of said angle B and the orientation ofsaid electron-optical axis causes said electron-formed visible image tohave an orientation and non-linear magnification distortion effective tosubstantially compensate for the off-axis-induced, non-linearmagnification distortion of the light image projected thereby on saidviewing screen.